ACOUSTIC TELEGRAPHY. 
37 
through the strip R, as shown in the right-hand figure. The 
shape of this little hook must be noticed. It will be seen at c 
that it has the form of a small triangle, making a sort of 
inclined plane drawn upwards by the weight of the disc, and is 
readily disengaged by a slight movement of the strip R. Of 
course, the signal is marked with the number of the subscriber 
with whose wire it communicates. Our subscriber No. 5, who 
has been waiting all this time, may now if he please make the 
call. He has only to blow into his apparatus, and then, in 
consequence of the comparatively powerful electric currents 
Fig. 10. 
which pass through the bobbins B, the strip r is thrown into 
vibrations ; and at each vibration it leaves the hook c, and this 
is enabled to rise a little at each movement. After a few 
vibrations it becomes completely free, and the disc, no longer 
kept back, falls and shows itself at the window, indicating that 
No. 5 has called and is waiting. 
Is not all this remarkably ingenious ? Observe, the disc is 
not shown unless the trumpet be used ; it does not fall by 
merely speaking, for the vibrations then produced are insuffi¬ 
cient. This indicates the difference between the molecular 
vibrations derived from articulate speech, and the more per¬ 
ceptible vibrations arising from musical sounds. 
The apparatus, however, is not now constructed exactly as 
